TLM 102 whining noise

[jodaki]

Hi, I've got a TLM 102 which I remember being a pretty quiet mic. I lent it to a friend and it was very noisy with his gear. I assumed it was his cables and brought it back here to test.

Strangely, when plugged in to a Mllennia HV-3D it makes a whiney noise - bit like a mosquito.

When plugged in to an ISA 428 it is also noisy, like at my friend's house, making a mains hum sort of noise.

However, when plugged into an ISA 428, Silver Bullet and Overstayer preamps, it it silent!

Can anyone suggest what might be going on?

Many thanks, John

[Hugh Robjohns]

Sounds like its picking up interference and/or its not being grounded properly. Id experiment with different cables (and connectors) as a starting point. You may well find the noises go away when used with a premium cable fitted with Neutrik, Switchcraft or Cannon connectors.

[jodaki]

Thanks Hugh, I love an experiment

1. the cable is professionally made and quite new (yes uses neutrik xlrs).
2. I experimented with sources of interference and not found any significant difference (to the problem) due to location or provocation in the form of mobile phone signal and computer.

- the same cable is as quiet as expected when used with an OC818 or C414 into the same preamps.

Here's a sound file of the issue.
https://www.kilroyjames.co.uk/ftp/tlm102-noise.mp3
It contains 4 short examples of:

1. TLM102 plugged in to HV-3D
2. TLM 102 plugged in to ISA 424
3. TLM plugged in to ISA 428
4. Swapped the mic for an OC818 and re-recorded through the ISA 428.

Same cable in all recordings. Same gain on all preamps (about 50db). Any fancy preamp stuff turned off (signal path as simple as I can make it). 12db gain applied to recording so you can hear it better.

[Hugh Robjohns]

Okay... well if you're confident that the cables and connectors are good, and interference isn't an issue, the next experiment would be to check the phantom power voltage. If the phantom power was low or inadequate in some way the mic's internal DC-DC converters might be struggling, resulting in audible whines/hums.

So, check the phantom voltage at the preamp connector with nothing connected. Measuring between pin 1 and pin 2 (or 3) it should be between 44 and 52V DC, but ideally close to 48V.

Then connect the mic and check the voltage again at the mic's XLR (you'll need to open the plug, obviously). It will be lower due to the mic drawing current through the 6k8 feed resistors.

The Neumann specs say the TLM102 draws 3.5mA. If that's per leg then by my calculation, you should see at least 20V at the mic XLR with the mic connected, and more likely 24V if the supply is actually 48V.

(If the 3.5mA figure is a total from both legs, then you'll see a minimum of 32V, but more likely 36V.)

It would be very unusual to have a phantom power problem, especially on more than one preamp, but it's an easy thing to check and rule out.

[jodaki]

Thanks Hugh, ok I did the tests with the TLM102 and an OC818 as control:

ISA 428
Preamp Connector : 48.6 V
OC818 : 41.6 V
TLM 102: 37.5

ISA 424
Preamp Connector : 48.6 V
OC818 : 41.7 V
TLM 102 : 37.3 V

HV-3D
Preamp Connector : 48.6 V
OC818 : 44.7 V
TLM 102: 46.2 V

How does that look? From what you were saying, the TLM 102 looks to be getting correct volts from the focusrites but a bit more from the Millennia.

I'm noticing that the two ISAs show almost identical readings but one of them sounds terrible while the other sounds as good as you could expect. Could there be a subtle fault with the mic that the 424 is 'auto-correcting' but the 428 and HV-3D are not?

[jodaki]

Hi, If this is a mic fault, can anyone suggest a good place to get it fixed in the UK? Or should I send it to Neumann? thanks, John

[Hugh Robjohns]

Best to send to Neumann Germany if it really needs attention, but I think we need some further consolidation of facts first... not least because your first post repeats ISA 428 rather than specify whether it whines with the ISA 424 or 428 (or both).

So... let's confirm which preamps it whines with, and which it doesn't -- using the same good quality and neutrik-connector cable for all.

It's also important that you're testing all preamps in the same location, and all are properly grounded (either via the mains cable (three-pin IEC) or via whatever the audio output is connected to.

And any ground-lift feature is not activated.

It appears from your earlier post that phantom supplies are all fine ...although I'm slightly perplexed by the high HV3D figure at the mic — it suggests an active constant-current phantom supply rather than the simple 6k8 resistors most devices use.

Another possibility to investigate: the newer HV3D and ISA units use switch mode power supplies, I think, and I'm wondering if the mic might be susceptible to HF interference from those.

If so, it might be worth trying a modified XLR cable as mentioned in my first reply. Open the female (mic end) XLR and ink the cable screen to the shell terminal instead of, or in addition to, pin-1.

It might also be worth trying a clip-on Ferrite ring, if you can get one of a suitable diameter for your mic cable. Fit one at the preamp end of BOTH the mic input and line output cables, AND the mains cable.

There's four sets of 5 different sizes on Amazon here for a tenner: https://amzn.eu/d/fLnIVXq

[jodaki]

Thanks for the reply Hugh, yes, sorry I made typo in my first post!

so to clarify:

ISA 428 mkII - no strange noises. mic works ok in this preamp.

ISA 430 mkII - shows a very prominent hum. sounds like a mains hum to me.

HV-3D - makes a whining/mosquito-like noise. analyser shows peaks at 530hz, 1060 hz and 1.6Khz

In the sound file I linked in my first post the order of preamps is:

HV-3D,
ISA 428,
ISA 430,
ISA 430 using OC818 mic instead of the TLM

All those three preamps are in the same rack and have their own power supply on a different ring circuit to the interface, speakers, computer and other stuff.

Preamps are grounded well as far as I can tell, via the mains.

For what it's worth I havent changed the rack setup in a few years and the TLM used to work fine through it. Though to be honest I cannot remember if I ever used it with the 430 or HV3D.

I will check your other suggestions and get back to you. Thanks again, John

[Sam Spoons]

Thanks for the reply Hugh, yes, sorry I made typo in my first post!

so to clarify:

ISA 428 mkII - no strange noises. mic works ok in this preamp.

ISA 430 mkII - shows a very prominent hum. sounds like a mains hum to me.

HV-3D - makes a whining/mosquito-like noise. analyser shows peaks at 530hz, 1060 hz and 1.6Khz

In the sound file I linked in my first post the order of preamps is:

HV-3D,
ISA 428,
ISA 430,
ISA 430 using OC818 mic instead of the TLM

All those three preamps are in the same rack and have their own power supply on a different ring circuit to the interface, speakers, computer and other stuff.

Preamps are grounded well as far as I can tell, via the mains.

For what it's worth I havent changed the rack setup in a few years and the TLM used to work fine through it. Though to be honest I cannot remember if I ever used it with the 430 or HV3D.

I will check your other suggestions and get back to you. Thanks again, John

[Hugh Robjohns]

Preamps on a different mains outlet to the interface shouldn't be an issue with balanced connections, and if the issue was ground loop noise it would affect all mics (and even no mics) rather than just the TLM102.

[Sam Spoons]

But on a different ring (not outlet)? Definitely worth a try powering everything off the same ring at least.

[Hugh Robjohns]

Still shouldn't matter, and would affect all mics not just one. No harm in trying your suggestion, but I dont think it's the issue we're looking for.

[jodaki]

Hi Hugh,

I bought the ferrite rings and clipped them as you suggested.

On the female mic end of the XLR cable I soldered a bit of cable between pin1 and the shell terminal. I didn't do this at the male end, I don't know if should have done.

I still have the loud mains-type noise from the ISA 430 and the mosquito from the HV-3D. I tried the mic in all 8 millennia inputs and they all do it.

Can you think of anything else to try?
Thanks, John

[Folderol]

Is the interference the same, with the mic hand held, on a stand, or just resting on some insulating surface? If not it might be its case (or an internal shield) poorly grounded - especially if it's at it's worst when hand held.

[jodaki]

Hi thanks Folderol, yes it is constant no matter where in the room the mic is, whether it's held or on a stand, or a wooden sideboard. I've held it next to the power outlets, the equipment, the lights etc. I can't hear a difference